High genetic diversity and possible evidence of a recent bottleneck in Adriatic bottlenose dolphins (Tursiops truncatus)

The bottlenose dolphin (Tursiops truncatus) is the only resident marine mammal species in the Croatian part of the Adriatic Sea, with an estimated number at around 220 individuals. It is an endangered and legally protected species in Croatia, and its demographic history is poorly known. This study investigates the level of genetic diversity in the bottlenose dolphin population from the Croatian part of the Adriatic Sea and a possibility of recent population size contraction, since there are indications that there has been intensive eradication operations in the mid 20th century that might have caused reductions in the effective population size and might have resulted in a loss of genetic variation. Thirty samples were genotyped at 12 dinucleotide microsatellite loci. The mean allelic richness (6.835 ± 0.705) and mean expected heterozygosity (0.692 ± 0.05) revealed high level of genetic diversity. Bottleneck analysis gave ambiguous evidence for a recent population decline in the investigated bottlenose dolphin population. The M ratio test, with two sets of parameter values, suggested a recent bottleneck; whereas the analysis by the Bottleneck program under three mutation models (TPM, SMM and IAM) showed no evidence for a genetic bottleneck. We take a more conservative approach to the interpretation of these results by accepting the evidence of a recent bottleneck. We suggest maintaining the current level of bottlenose dolphin protection in the area and careful monitoring of the population in the future.